The continued sustained threat of the SARS-CoV-2 virus world-wide, urgently calls for far-reaching effective therapeutic strategies for treating this emerging infection. Accordingly, this study explores mode of action and therapeutic potential of existing antiviral drugs. Multiple sequence alignment and phylogenetic analyses indicate that the RNA-dependent RNA polymerase (RdRp) of SARS-CoV-2 was mutable and similar to bat coronavirus RaTG13. Successive interactions between RdRp (nsp12 alone or in complex with cofactors nsp7-8) and viral RNA demonstrated that the binding affinity values remained the same, but the sites of interaction of RdRp (highly conserved for homologous sequences from different organisms) were altered in the presence of selected antiviral drugs such as Remdesivir, and Sofosbuvir. The antiviral drug Sofosbuvir reduced the number of hydrogen bonds formed between RdRp and RNA. Remdesivir bound more tightly to viral RNA than viral RdRp alone or the nsp12-7-8 hexadecameric complex, resulting in a significant number of hydrogen bonds being formed in the uracil-rich region. The interaction between nsp12-7-8 complex and RNA was mediated by specific interaction sites of nsp7-8. Therefore, the conserved nature of RdRp interaction sites, and alterations due to drug intervention indicate the therapeutic potential of the selected drugs. In this article, we provide additional focus on the interacting amino acids of the nsp7-8 complex and highlight crucial regions that could be targeted for precluding a correct recognition of subunits involved in the hexadecameric assembly, to rationally design molecules endowed with a significant antiviral profile.

Background: The alarming increase in the number of SARS-CoV-2 cases worldwide, urgently demands far-reaching effective strategies to win the battle against emerging as well as re-emerging diseases. Many research laboratories are conducting clinical trials with different drugs, among which some became quite interestingly effective against this pandemic. Our aim is to investigate the potentiality of the pre-existing drugs and get a clear understanding of their effects on RNA-dependent RNA polymerase (RdRp) of the SARS-CoV-2. Methods: Multiple sequence alignment (MSA) alogwith molecular phylogeny analysis were performed using homologous sequences to identify the mutations within RdRp and evolutionary relationship. Based on the published literatures, we have chosen eight drug molecules like Ribavirin, Tenofovir, Sofosbuvir, IDX-184, YAK, Setrobuvir, Remdesivir and Galidesivir. Series of molecular docking studies between template RNA and RdRp of SARS-CoV-2 has been performed in absence or presence of those drugs and cofactors nsp7 and nsp8.Results: From MSA 13 exclusive mutations identified within RdRp of SARS-CoV-2 and phylogeny reveals its close relation with Bat coronavirus RaTG13. The interaction affinities and interacting residues as obtained from systematic molecular docking study led to a conclusion that the chosen drugs can prove to be effective against this pandemic partially. Conclusion: Therefore, designing of inhibitors which will specifically act against nsp12 and lower the binding affinity of nsp12 towards RNA template is necessary. In this article we additionally focus on the nsp7-8 hexadecameric complex and had suggested a list of amino acid residues of nsp12 and nsp7-8 complex to develop far-reaching effective drugs.